Instruments and methods for tensioning a spinal tether

ABSTRACT

Various methods and devices are provided for tensioning a tether. In one embodiment, a tether tensioning device is provided and includes an elongate shaft adapted to be positioned adjacent to a bone anchor implanted in bone, and a tensioning mechanism pivotally associated with the elongate shaft and adapted to couple to a tether seated across the bone anchor and to pivot relative to the elongate shaft to apply a tensioning force to the tether.

FIELD

The present application relates to devices and methods for tensioning atether extending between bone anchors implanted in bone.

BACKGROUND

Spinal deformities, which include rotation, angulation, and/or curvatureof the spine, can result from various disorders, including, for example,scoliosis (abnormal curvature in the coronal plane of the spine),kyphosis (backward curvature of the spine), and spondylolisthesis(forward displacement of a lumbar vertebra). Early techniques forcorrecting such deformities utilized external devices that apply forceto the spine in an attempt to reposition the vertebrae. These devices,however, resulted in severe restriction and in some cases immobility ofthe patient. Furthermore, current external braces have limited abilityto correct the deformed spine and typically only prevent progression ofthe deformity. Thus, to avoid this need, several rod-based techniqueswere developed to span across multiple vertebrae and force the vertebraeinto a desired orientation.

In rod-based techniques, one or more rods are attached to the vertebraeat several fixation sites to progressively correct the spinal deformity.The rods are typically pre-curved intraoperatively to a desired adjustedspinal curvature. Wires as well as bone screws can be used to pullindividual vertebra toward the rod. Once the spine has beensubstantially corrected, the procedure typically requires fusion of theinstrumented spinal segments.

While several different rod-based systems have been developed, they tendto be cumbersome, requiring complicated surgical procedures with longoperating times to achieve correction. Further, intraoperativeadjustment of rod-based systems can be difficult and may result in lossof mechanical properties due to multiple bending operations. Therigidity and permanence of rigid rod-based systems can also hinder orprevent growth of the spine and they generally require fusion of manyspine levels, drastically reducing the flexibility of the spine. To helpremedy some of these issues, a tether and anchor system can be used tocorrect curvature of the spine using a number of anchors disposed withinthe spinal bones connected with tethers extending between them. Theelasticity of the tethers prevents some of the problems with therigidity and permanence of the rod-based systems, although the tethersmust be tensioned after implantation to achieve the desired forcebetween the anchor to correct the spinal deformities.

Accordingly, there remains a need for improved methods and devices forcorrecting spinal deformities and, in particular, there remains a needfor methods and devices for tensioning a tether extending betweenanchors implanted in bone.

SUMMARY

Various methods and devices for tensioning a tether are provided. In oneembodiment, a tether tensioning device is provided and includes anelongate shaft adapted to be positioned adjacent to a bone anchorimplanted in bone. A tensioning mechanism can be pivotally associatedwith the elongate shaft and it can be adapted to couple to a tetherseated across the bone anchor and to pivot past a longitudinal axis ofthe elongate shaft to apply a tensioning force to the tether. Inparticular, the tensioning mechanism can be adapted to move from a firstposition in which the tensioning mechanism is pivoted away from theelongate shaft, to a second position in which the tensioning mechanismis pivoted past the longitudinal axis of the elongate shaft to apply atensioning force to a tether. In one exemplary embodiment, the elongateshaft can include an elongate slot formed therein. The elongate slot canbe adapted to receive the tensioning mechanism therethrough tofacilitate pivoting of the tensioning mechanism past the longitudinalaxis of the elongate shaft. Various techniques can be used to mate atether to the tensioning mechanism. For example, the tensioningmechanism can include one or more openings formed therethrough andadapted to receive a portion of a tether to allow the tether toremovably couple to the tensioning mechanism. The device can alsoinclude a handle coupled to a proximal end of the elongate shaft.

In one exemplary embodiment, the tensioning mechanism can also beadapted to move longitudinally along an axis of the elongate shaftbetween proximal and distal positions. The tether tensioning device canalso include a biasing element coupled to the tensioning mechanism andadapted to bias the tensioning mechanism to the proximal position. Forexample, the biasing element can be a spring disposed within theelongate shaft and coupled to a distal portion of the tensioningmechanism to bias the tensioning mechanism proximally. The spring can beadapted to be compressed to allow the tensioning mechanism to movedistally and to thereby control the amount of tensioning force appliedto a tether as the tensioning mechanism is moved to the second position.

In another embodiment, a tether tensioning device is provided andincludes an elongate shaft having a tensioning mechanism pivotallyassociated with the elongate shaft and adapted to couple to a tether toapply a tensioning force thereto. The device can also include anoverload mechanism coupled to the tensioning mechanism. The overloadmechanism can be adapted to allow the tensioning mechanism to movedistally along an axis of the elongate shaft when a threshold force isapplied to the tether. In one embodiment, the tensioning mechanism canbe pivotally coupled to a body that is slidably coupled to the elongateshaft, and the overload mechanism can be a biasing element that biasesthe body proximally along the elongate shaft. In an exemplaryembodiment, the overload mechanism can be in form of a spring disposedwithin the elongate shaft and coupled to a distal portion of thetensioning mechanism. The spring can be adapted to be compressed by thetensioning mechanism when a threshold force is applied to a tethercoupled to the tensioning mechanism. In order to apply the tensioningforce to the tether, the tensioning mechanism can be adapted to movefrom a first position in which the tensioning mechanism is pivoted awayfrom the elongate shaft, to a second position in which the tensioningmechanism is pivoted past a longitudinal axis of the elongate shaft toapply a tensioning force to a tether. In one embodiment, the tensioningmechanism can include one or more openings formed therethrough forreceiving a portion of the tether therethrough to allow the tether toremovably couple to the tensioning mechanism.

Methods for applying tension to a tether are also provided, and in oneembodiment the method can include coupling a tether seated across a boneanchor implanted in bone to a tensioning mechanism pivotally associatedwith an elongate shaft, and pivoting the tensioning mechanism past alongitudinal axis of the elongate shaft to apply a tensioning force tothe tether. Coupling the tether to the tensioning mechanism can includethreading a portion of the tether through one or more openings formed inthe tensioning mechanism. Pivoting the tensioning mechanism can includemoving the tensioning mechanism from a first position in which thetensioning mechanism is pivoted away from the elongate shaft, to asecond position in which the tensioning mechanism is pivoted past thelongitudinal axis of the elongate shaft to apply the tensioning force tothe tether. In one exemplary embodiment, the tensioning mechanism ispivoted past the longitudinal axis of the elongate shaft by pivotinginto a slot formed in the elongate shaft. The tensioning mechanism canoptionally be biased to a proximal position by a biasing element coupledto a distal end of the tensioning mechanism. When a threshold tensioningforce is applied to the tether, the tensioning mechanism moves distallyalong a longitudinal axis of the elongate shaft. In one embodiment, abiasing element can bias the tensioning mechanism proximally, and thebiasing element can be compressed as the tensioning mechanism movesdistally.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments disclosed herein will be more fullyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a perspective view of one embodiment of a tether tensioningdevice having a tensioning mechanism shown in a first, untensionedposition;

FIG. 2 is a perspective view of the tether tensioning device of FIG. 1showing the tensioning mechanism in a second, tensioned position;

FIG. 3 is a front view of the tether tensioning device of FIG. 2;

FIG. 4 is a perspective view of the tether tensioning device of FIG. 2showing a biasing element coupled to the tensioning mechanism;

FIG. 5 is a perspective view of the tensioning mechanism and biasingelement of FIG. 4 showing a tether coupled to the tensioning mechanismthat is in the first, untensioned position; and

FIG. 6 is a perspective view of the tensioning mechanism and biasingelement of FIG. 4 showing a tether coupled to the tensioning mechanismthat is in the second, tensioned position.

DETAILED DESCRIPTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the devices and methods disclosed herein. One ormore examples of these embodiments are illustrated in the accompanyingdrawings. Those skilled in the art will understand that the devices andmethods specifically described herein and illustrated in theaccompanying drawings are non-limiting exemplary embodiments and thatthe scope is defined solely by the claims. The features illustrated ordescribed in connection with one exemplary embodiment may be combinedwith the features of other embodiments. Such modifications andvariations are intended to be included within the scope of the presentapplication.

Various exemplary methods and devices are provided for tensioning atether extending across one or more anchors implanted in bone. Ingeneral, a tensioning mechanism is provided that is adapted to couple toa tether seated across one or more bone anchors implanted in bone. Thetensioning mechanism can be adapted to apply a tensioning force to thetether to allow the tether to be tensioned between the bone anchors.

FIGS. 1-3 illustrate one exemplary embodiment of a tether tensioningdevice 10 that generally includes an elongate shaft 12 extending from ahandle 14. A tensioning mechanism 16 is pivotally associated with theelongate shaft 12 and it is adapted to mate to a tether 18 seated acrossone or more bone anchors implanted in bone. The tensioning mechanism 16can be adapted to move from a first, untensioned position in which thetensioning mechanism 16 is pivoted away from the elongate shaft 12,shown in FIG. 1, to a second, tensioned position in which the tensioningmechanism 16 is pivoted toward the elongate shaft 12 and past alongitudinal axis of the elongate shaft 12 to apply a tensioning forceto the tether 18. In one exemplary embodiment, the tensioning mechanism16 can be pivoted into a slot 20 formed in the elongate shaft 12 toapply a tensioning force to the tether 18, shown in FIG. 2. A personskilled in the art will appreciate that the tensioning mechanism 16 canbe pivoted past the longitudinal axis of the elongate shaft 12 in avariety of ways, including but not limited to the tensioning mechanism16 being moved around a side of the elongate shaft 12, over an end ofthe elongate shaft 12, or up into the elongate shaft 12.

The elongate shaft 12 can have a variety of configurations, and it canbe flexible or rigid depending on the intended use. In an exemplaryembodiment, the elongate shaft 12 has a length that allows the distalend 12 d of the elongate shaft 12 to be positioned adjacent to a tether18 disposed along a spinal column, while the proximal end 12 p remainsexternal to the body. This length allows the elongate shaft 12 to extendfrom the tissue surface to the treatment site, e.g., bone anchorsimplanted in vertebrae. A person skilled in the art will appreciate thatthe elongate shaft 12 can be made from a variety of biocompatiblematerials that have properties sufficient to enable the elongate shaft12 to be inserted into the body. As further shown in FIGS. 1-3, theelongate shaft 12 can also include a slot 20 formed therein. The slot 20can be configured to receive a portion of the tensioning mechanism 16when the tensioning mechanism 16 is moved to the second position, aswill be discussed in more detail below. Thus, the particular locationand size of the slot 20 can vary depending on the location and size ofthe tensioning mechanism 16. In the illustrated embodiment, the slot 20is located in a proximal portion of the elongate shaft 12, just proximalto the mating location between the tensioning mechanism 16 and theelongate shaft 12, and it extends along about half or less than half ofthe length of the elongate shaft 12. A person skilled in the art willappreciate that the slot 20 can have various configurations and it canbe at a variety of locations on the elongate shaft 12.

The elongate shaft 12 can also include a handle 14 formed on or coupledto the proximal end 12 p of the elongate shaft 12. The handle 14 canhave any shape and size but it is preferably adapted to facilitategrasping and manipulation of the device 10. As shown in FIG. 1, thehandle 14 has a generally elongate cylindrical configuration and extendssubstantially perpendicular to the longitudinal axis of the elongateshaft 12. A person skilled in the art will appreciate that any handlecan be coupled to the elongate shaft, or that the device 10 can be usedwithout a handle.

As indicated above, the device 10 also includes a tensioning mechanism16, shown in more detail in FIGS. 4-6, that is associated with theelongate shaft 12 and that is adapted to apply a tensioning force to atether 18. The tensioning mechanism 16 can have a variety of shapes andsizes, but it is preferably adapted to grasp or mate to a tether 18 andto apply a tensioning force to the tether 18. While the tensioningmechanism 16 can have a variety of configurations, in one exemplaryembodiment, as shown, the tensioning mechanism 16 is in the form of anarm that is pivotally coupled to the elongate shaft 12. The tensioningmechanism 16 can be pivotally coupled to the elongate shaft in a varietyof ways. For example, in the illustrated embodiment, a distal end 16 dof the tensioning mechanism 16 includes two legs that are pivotallycoupled to first and second pivot bosses 24 a, 24 b disposed on theelongate shaft 12 at first and second pivot points 26 a, 26 b. Thebosses 24 a, 24 b are located just distal to a distal end of theelongate slot 20. A person skilled in the art will appreciate, however,that the tensioning mechanism 16 can be coupled to the elongate shaft 12in any way that allows it to pivot with respect to the elongate shaft12. Moreover, a person skilled in the art will appreciate that thetensioning mechanism 16 can be removable from the elongate shaft 12. Thetensioning mechanism 16 can be pivotally attached to the elongate shaft12 in a variety of ways, including nesting the tensioning mechanism 16into the elongate shaft 12, or coupling the tensioning mechanism 16 tothe bosses 24 a, 24 b disposed on the elongate shaft 12. In addition,the tensioning mechanism 16 can be positioned along the elongate shaft12 at a variety of locations, but it is preferably positioned at alocation that allows the tensioning mechanism 16 to be pivoted into theelongate slot 20, and that allows the tensioning mechanism 16 to bemanipulated by a user when the distal end of the elongate shaft 12 ispositioned adjacent to a tether 18 implanted in the spine.

The tensioning mechanism 16 can also include features to allow thetether 18 to be coupled thereto. In one embodiment, the tensioningmechanism 16 can include one or more openings 22 formed therethrough.The openings 22 can have any size and shape, but are preferably of asize and shape that facilitate threading the tether 18 therethrough. Aperson skilled in the art will appreciate that any features can be usedto couple the tether 18 to the tensioning mechanism 16, including anytype of opening or grasping mechanism formed on the tensioning mechanism16. In one embodiment, where the tensioning mechanism 16 is removablefrom the elongate shaft 12, the tether 18 can be pulled to the correctlength by hand, and then coupled to the tensioning mechanism 16, forexample, through the openings 22.

In order to apply the tensioning force to the tether 18, the tensioningmechanism 16 is adapted to pivot from a first, untensioned position inwhich the tensioning mechanism 16 is spaced apart from and extendstransverse to the elongate shaft 12, as shown in FIG. 1, to a second,tensioned position in which the tensioning mechanism is pivoted into theslot 20 to apply a tensioning force to a tether 18. In particular, asthe tensioning mechanism 16 is moved to the second position, the tether18 is pulled proximally and then pulled through the slot 20. In order tomaintain the tensioning force applied to the tether 18 when thetensioning mechanism 16 is pivoted into the second, tensioned position,the tensioning mechanism 16 can be adapted to pivot in such a way as toallow at least a portion of the tensioning mechanism 16 to extendcompletely through the slot 20 formed in the elongate shaft 12, as shownin FIG. 2. In other words, the tensioning mechanism 16 moves across thelongitudinal axis and is positioned on an opposite side of the elongateshaft 12. As a result, a portion of the tether 18 coupled to thetensioning mechanism 16 is positioned past the pivot points 26 a, 26 band is being pulled with a downward force. This downward force maintainsthe tensioning mechanism 16 in the second, tensioned positioned, thusmaintaining the tensioning force applied to the tether 18. A personskilled in the art will appreciate that a variety of other techniquescan be used to maintain the tensioning mechanism 16 is the secondposition, including various locking mechanisms.

The tensioning mechanism 16 can also includes features to control theamount of tensioning force that is applied to the tether 18. In theillustrated embodiment, an overload mechanism is coupled to thetensioning mechanism 16 and it is adapted to allow the tensioningmechanism 16 to move distally along an axis of the elongate shaft 12between a proximal position and distal position when a threshold forceis applied to the tether 18. This prevents a tensioning force greaterthan the threshold force from being applied to the tether 18.

The overload mechanism can have a variety of configurations, but in oneembodiment it can be in the form of a biasing element, such as a spring28, for biasing the tensioning mechanism 16 proximally. The spring 28can be disposed in a channel 31 formed in the elongate shaft 12,preferably at a position distal of the elongate slot 20. A proximal endof the spring 28 can be coupled to a distal end of the tensioningmechanism 16, and in particular the proximal end of the spring 28 canabut against a distal surface of a body 32 have the bosses 24 a, 24 bformed thereon. The body 32 can be movably disposed within the channel31. In order to maintain the body 32 and the spring 28 in the channel31, the channel 31 can include an elongate rod 34 disposed therein andextending through the spring 28 and through a bore 36 in the body 32.This will allow the body 32, and thus the tensioning mechanism 16, tomove proximally and distally within the channel 31, thereby compressingand relieving the spring 28. A distal end of the spring 28 can restagainst a distal portion of the channel 31 formed in the elongate shaft12. In use, the biasing force of the spring 28 on the tensioningmechanism 16 can be overcome by pivoting the tensioning mechanism 16until the tensioning force being applied to the tether 18 reaches thethreshold force. This causes the tensioning mechanism 16 to movedistally and thereby compress the spring 28, thus preventing anyadditional tensioning force from being applied to the tether 18. Thetension of the spring 28 can be selected based on the desired thresholdforce. For example, a tightly-wound spring will yield a higher thresholdforce than a loosely-wound spring. A person skilled in the art willappreciate that a variety of other biasing elements can be used tocontrol the amount of tensioning force being applied to the tether 18.

In use, the device 10 can be inserted through tissue, or through anaccess port disposed in tissue, so that the handle 14 and the tensioningmechanism 16 can extend from the tissue or port on the outside, and thedistal end of the device 10 can be positioned adjacent to a bone anchor.The device 10 can be positioned adjacent to a tether 18 extendingbetween bone anchors to be tensioning. For example, the device 10 can beremovably mated to the bone anchor, or it can be positioned against aside of the bone anchor, or spaced apart from the bone anchor. A freeend of the tether 18 can be grasped using a grasping device to allow thetether 18 to be removed from the body and coupled to the tensioningmechanism 18, as shown in FIG. 5. Once the tether 18 is coupled to thetensioning mechanism 16, the tensioning mechanism 16 can be pivotedtowards the elongate shaft 12 and into and through the slot 20 to causea tensioning force to be applied to the tether 18, as shown in FIG. 6.If the tensioning force being applied to the tether 18 reaches athreshold force based on the tension of the spring 28 coupled to thetensioning mechanism 16, the spring 28 will collapse, allowing thetensioning mechanism 16 to move distally along the elongate shaft 12.This is effective to prevent the tensioning force being applied to thetether 18 from being greater than the threshold force.

Once the proper tension is applied to the tether 18, and the tether 18has been locked to the bone anchor(s) to retain the tension thereonafter the device 10 is removed, the device 10 can be removed. In oneembodiment, the tether can be locked between adjacent bone anchors byapplying a locking mechanism, such as a set screw, to each bone anchor.A person skilled in the art will appreciate that any mechanism can beused to lock the tensioned tether 18 between adjacent bone anchors.

A person skilled in the art will appreciate that the various methods anddevices disclosed herein can be formed from a variety of materials.Moreover, particular components can be implantable and in suchembodiments the components can be formed from various biocompatiblematerials known in the art. Exemplary biocompatible materials include,by way of non-limiting example, composite plastic materials,biocompatible metals and alloys such as stainless steel, titanium,titanium alloys and cobalt-chromium alloys, and any other material thatis biologically compatible and non-toxic to the human body.

One skilled in the art will appreciate further features and advantagesbased on the above-described embodiments. Accordingly, the disclosure isnot to be limited by what has been particularly shown and described,except as indicated by the appended claims. All publications andreferences cited herein are expressly incorporated herein by referencein their entirety.

What is claimed is:
 1. A tether tensioning device, comprising: anelongate shaft adapted to be positioned adjacent to a bone anchorimplanted in bone; and a tensioning mechanism having a first portionpivotally associated with the elongate shaft and a second portionadapted to couple to a tether seated across the bone anchor, wherein thetensioning mechanism is positionable such that the first portion isdisposed on one side of the elongate shaft and at least a portion of thetensioning mechanism is disposed on an opposite side of the elongateshaft; wherein the tensioning mechanism is adapted to move from a firstposition in which the second portion of the tensioning mechanism ispivoted away from the elongate shaft, to a second position in which thesecond portion of the tensioning mechanism is pivoted toward and throughthe elongate shaft such that the at least a portion of the tensioningmechanism is disposed on an opposite side of the elongate shaft as thefirst portion to apply a tensioning force to the tether.
 2. The deviceof claim 1, wherein the tensioning mechanism is adapted to movelongitudinally along an axis of the elongate shaft between proximal anddistal positions.
 3. The device of claim 2, further comprising a biasingelement coupled to the tensioning mechanism and adapted to bias thetensioning mechanism to the proximal position.
 4. The device of claim 3,wherein the biasing element comprises a spring disposed within theelongate shaft and coupled to the tensioning mechanism to allow thetensioning mechanism to move longitudinally along a portion of theelongate shaft.
 5. The device of claim 4, wherein the spring is adaptedto be compressed to control the amount of tensioning force applied to atether as the tensioning mechanism is moved to the second position. 6.The device of claim 1, further comprising a handle coupled to a proximalend of the elongate shaft.
 7. The device of claim 1, wherein the secondportion of the tensioning mechanism includes one or more openings formedtherethrough and adapted to receive a portion of a tether to allow thetether to removably couple to the tensioning mechanism.
 8. The device ofclaim 1, wherein the elongate shaft includes an elongate slot formedtherein, the elongate slot being adapted to receive the tensioningmechanism therethrough.
 9. A tether tensioning device, comprising: anelongate shaft having a tensioning mechanism pivotally associatedtherewith at a pivot point and adapted to couple to a tether such thatthe tensioning mechanism applies a tensioning force thereto in aproximal direction; and an overload mechanism coupled to the tensioningmechanism and adapted to allow the pivot point of the tensioningmechanism to move in a distal direction relative to the elongate shaftalong an axis of the elongate shaft in response to a thresholdtensioning force applied to the tether.
 10. The device of claim 9,wherein the tensioning mechanism is pivotally coupled to a body that isslidably coupled to the elongate shaft.
 11. The device of claim 10,wherein the overload mechanism comprises a biasing element that biasesthe body proximally along the elongate shaft.
 12. The device of claim10, wherein the tensioning mechanism comprises an elongate arm havingproximal and distal ends, the distal end of the tensioning mechanismbeing pivotally coupled to the body.
 13. The device of claim 10, whereinthe elongate shaft includes a first opening configured to receive atleast a portion of the tensioning mechanism and a second opening havingthe body disposed therein.
 14. The device of claim 9, wherein theoverload mechanism comprises a spring disposed within the elongate shaftand coupled to the tensioning mechanism, the spring being adapted to becompressed when a threshold force to applied to a tether.
 15. A methodof applying a tensioning force to a tether extending along a spinalcolumn, comprising: coupling a tether seated across a bone anchorimplanted in bone to a first portion of a tensioning mechanism, thetensioning mechanism having a second portion pivotally associated withan elongate shaft; and pivoting the first portion of the tensioningmechanism such that the second portion of the tensioning mechanism isdisposed on a first side of the elongate shaft and at least a portion ofthe tensioning mechanism is disposed on a second, opposite side of theelongate shaft, thereby applying a tensioning force to the tether;wherein pivoting the first portion of the tensioning mechanism includesmoving the tensioning mechanism from a first position in which the firstportion of the tensioning mechanism is pivoted away from the elongateshaft, to a second position in which the first portion of the tensioningmechanism is pivoted past a longitudinal axis of the elongate shaft andthe at least a portion of the tensioning mechanism is disposed on thesecond, opposite side of the elongate shaft to apply the tensioningforce to the tether.
 16. The method of claim 15, wherein coupling thetether to the first portion of the tensioning mechanism includesthreading a portion of the tether through one or more openings formed inthe first portion of tensioning mechanism.
 17. The method of claim 15,wherein the first portion of the tensioning mechanism is pivoted pastthe longitudinal axis of the elongate shaft by pivoting into a slotformed in the elongate shaft.
 18. The method of claim 15, wherein, whena threshold tensioning force is applied to the tether, the tensioningmechanism moves distally along a longitudinal axis of the elongateshaft.
 19. The method of claim 18, wherein a biasing element biases thetensioning mechanism proximally, and the biasing element is compressedas the tensioning mechanism moves distally.